CN109014198A - A method of preparing the pure molybdenum part of high-performance - Google Patents

Abstract

A method of no mold prepares the pure molybdenum part of high-performance, belongs to powder increases material manufacturing technology field.The molybdenum powder of good fluidity is obtained using airflow milling technical treatment three times first, treated molybdenum powder particle is by aggregating state to dispersity, narrower to subsphaeroidal and particle diameter distribution by irregular polymorph, to meet the requirement of increasing material manufacturing technique.Then by molybdenum powder in a hydrogen atmosphere reduction treatment to reduce its oxygen content.Meanwhile going out the workpiece schematic diagram and optimal Processing Strategies (such as scanning speed, sweep span, Scan slice thickness and scanning direction) of complicated shape by computer modeling software design, derived parameter file realizes modeling.Molybdenum powder after reduction is packed into SLM precinct laser fusion equipment and imports Parameter File, prepares the molybdenum part of final complicated shape.The invention significantly optimizes raw material powder and SLM machined parameters, reduces energy consumption, and the molybdenum part prepared is excellent close to full densification, uniform texture, comprehensive mechanical property.

Description

A method for preparing high-performance pure molybdenum metal parts

technical field

The invention belongs to the technical field of powder additive manufacturing, and particularly provides a method for preparing high-performance pure molybdenum metal parts.

Background technique

Molybdenum has high melting point, low saturated vapor pressure, small linear expansion coefficient, high temperature strength, small specific resistance and film stress, good acid and alkali resistance and good environmental performance; Screen, vacuum coating and other fields have a wide range of applications. The manufacture of molybdenum metal parts usually adopts the traditional powder metallurgy process, that is, "preparation of molybdenum powder - cold isostatic pressing - induction sintering - deformation treatment". The high melting point of molybdenum makes it difficult to sinter and densify molybdenum powder, which requires a higher sintering temperature. It causes large manufacturing energy consumption; and often requires more machining and post-processing when manufacturing parts with complex shapes. The sintering temperature of the powder metallurgy method has a great influence on the structure, the temperature is different, the structure is different, and the grain size is also different. Crucibles, molds, etc. are required for powder compaction, which are likely to cause pollution and make it difficult to prepare high-purity molybdenum slabs. Not only that, it is also difficult to prepare molybdenum metal parts with complex shapes and specific dimensions using molds. Selective laser melting technology has been widely used in the field of preparing pure Mo metal parts with various shapes. Selected laser melting (SLM) is a new type of AM/3D printing technology, which has unique advantages such as mold-free production and rapid preparation of three-dimensional parts of any shape. However, there are two problems in the preparation of molybdenum metal parts by selective laser melting: easy cracking and low density, which greatly increases the difficulty of material preparation and processing, and the manufacturing cost of parts is very high. There are two main reasons why it is difficult to prepare highly dense and high-performance 3D printing pure molybdenum products: one is that 3D printing often needs to use spherical powders with very good fluidity, and the existing molybdenum powders have serious agglomeration and poor fluidity, so it is not suitable Directly used in laser rapid prototyping. Although the plasma spheroidization process can produce spherical molybdenum powder with high sphericity, the yield of spherical powder is low, the powder particle size distribution is uneven, and the preparation cost is high. Therefore, the preparation technology of molybdenum powder with uniform particle size distribution and low oxygen content is limited. The second is the "spheroidization" phenomenon (resulting in low density of the product) and the "grid crack" phenomenon in the SLM preparation process of molybdenum.

Contents of the invention

The object of the present invention is to provide a method for preparing high-performance pure molybdenum metal parts with complex shapes by using the selective laser melting (SLM) technology. Using high-purity polycrystalline molybdenum powder as raw material, by changing the molybdenum powder particles from agglomerated state to dispersed state, from irregular polycrystalline to nearly spherical and narrower particle size distribution, in order to meet the high fluidity of the powder in the additive manufacturing process Require. The method helps to solve the problems of difficult densification and high processing difficulty of molybdenum products, and can also significantly reduce powder preparation costs and process energy consumption.

A method for preparing high-performance pure molybdenum metal parts, which is characterized in that: firstly, the nearly spherical molybdenum powder with uniform dispersion and narrow particle size distribution is obtained by multiple jet milling technology, and then the molybdenum powder is reduced in a high-temperature furnace in a hydrogen atmosphere , to obtain reduced molybdenum powder with low oxygen content and good fluidity; mix the nearly spherical molybdenum powder with different particle sizes after jet milling; at the same time, use computer modeling software to design a schematic diagram of a workpiece with a complex shape and control the scanning speed, scanning distance, Scan the layer thickness and scanning direction, and export the print file; clean the powder feeding tank and printing room of the selective laser melting equipment to ensure that the printing environment is clean and pollution-free; then, load the powder into the SLM device and import the printing file to prepare complex shapes of molybdenum metal piece, the preparation process is as shown in Figure 1, and the specific process steps are:

1. Jet milling treatment of molybdenum powder: The raw material powder is polycrystalline molybdenum powder with different particle sizes, and a counter-jet jet milling device is used. The pressure of the grinding chamber is set at 0.5-1.0 MPa, nitrogen is used as the grinding medium, the oxygen content in the grinding chamber is ≤0.05%, and the molybdenum powder is processed within the frequency range of the sorting wheel of 15-60 Hz. Three jet milling processes are adopted, that is, the first jet mill disperses and shapes the molybdenum powder at a high frequency of 45-60 Hz, the second jet mill disperses and shapes the molybdenum powder at an intermediate frequency of 30-45 Hz, and the third jet mill The molybdenum powder is further shaped and particle size sieved at a low frequency of 15-30Hz to make the surface of the powder smoother and further improve the fluidity of the powder. The jet mill finally obtains a nearly spherical molybdenum powder with narrow particle size distribution and good dispersion;

2. Powder reduction: Put the mixed molybdenum powder processed by jet mill into a tube furnace, feed high-purity hydrogen, and reduce it for 60-120 minutes at 600-650°C and a heating rate of 7°C/min to obtain hypoxia content of molybdenum powder;

3. Modeling: first draw the three-dimensional schematic diagram of the part with 3D Max software, then set the processing parameters, and export the parameter file in the Materialize Magics software. The processing parameters are characterized by laser energy density, as shown in Figure 2;

4. Selective laser melting (SLM) forming: first import the model file into the computer system of the SLM selective laser melting equipment, load the reduced jet-milled molybdenum powder into the powder feeding tank, and then spread a layer of powder with a thickness of about 50 μm on the molybdenum substrate , using high-purity argon for protection, and the laser scanning can be started only after the oxygen content in the construction room is ≤0.05%, so as to realize the full-automatic printing and forming. Finally, complex shaped and highly dense (>98%) molybdenum metal parts are obtained.

Further, the target high-density molybdenum metal piece has a purity of more than 99.99% and a density of more than 98%.

Furthermore, the molybdenum powder processed by the three-time jet milling process has a narrow average particle size distribution, good powder dispersion, a nearly spherical shape, good fluidity, increased specific surface area, improved sintering activity, and a good molten pool can be obtained. print quality.

Further, the oxygen content of the molybdenum powder after reduction in a tube furnace is ≤0.01%.

Further, the various working parameters of SLM are: laser power E is 380W, scanning speed is 200-700mm/s, scanning distance is 80-120μm, scanning layer thickness is 30-50μm, oxygen content in the construction cabin is ≤0.05%, scanning strategy adopts 45°rotation Alternate grid scanning can weaken crack propagation behavior, balance residual stress, and obtain high-performance pure molybdenum metal parts.

From the perspective of optimizing the raw material powder, the present invention performs jet milling treatment on the raw material molybdenum powder, enhances the fluidity of the raw material powder, improves the laser absorption rate of the powder, and realizes densification. And design the optimal preparation and processing parameters for modeling, using the selective laser melting (SLM) 3D printing technology, design a specific scanning strategy to weaken the crack propagation behavior, balance the residual stress, improve the material performance, and prepare high-performance materials with complex shapes. Pure molybdenum metal parts.

The main technical advantages of this technical solution are:

(1) The raw material polycrystalline molybdenum powder can be processed by jet mill to obtain nearly spherical molybdenum powder, which can change the fluidity of the molybdenum powder, increase the specific surface area, improve the sintering activity, fully melt the molybdenum powder, obtain a good molten pool, and improve the printing quality;

(2) The oxygen content of molybdenum powder can be further reduced by hydrogen reduction in tube furnace.

(3) For the first time, the scanning strategy of 45° rotating alternating grid pattern is used to weaken the crack propagation behavior, balance the residual stress, and prepare high-performance pure molybdenum metal parts with complex shapes.

Description of drawings

Fig. 1 is a process flow diagram of the present invention;

Figure 2 is a schematic diagram of the laser scanning strategy.

Detailed ways

The present invention will be further elaborated below in conjunction with example, but the present invention is not limited to specific embodiment.

Example 1

The raw material powder is polycrystalline molybdenum powder with an average particle size of about 15 μm, a total of 15 kg, and a counter-jet jet milling device is used. The pressure of the grinding chamber is set at 0.5-1.0 MPa, and nitrogen gas is used as the grinding medium so that the oxygen content in the grinding chamber is ≤0.5%. The first jet mill is processed at 45-60Hz, the second jet mill is treated at 30-45Hz, the third jet mill is treated at 15-30Hz, and finally a nearly spherical molybdenum powder with an average particle size of about 10μm is obtained. The obtained molybdenum powder is put into a tube furnace, fed with high-purity hydrogen, and reduced for 60-120 minutes under the conditions of 600-650°C and a heating rate of 7°C/min. Use 3D Max software to draw a three-dimensional schematic diagram of the part, then set the processing parameters, and export the parameter file in Materialize Magics software. Clean the feed tank, powder feeder, powder spreader and substrate with absolute ethanol, and blow dry with a hair dryer. Purge the build chamber and residue recovery tube with an argon gun. The reduced mixed molybdenum powder is loaded into the powder feeding tank, and then a layer of powder with a thickness of about 50 μm is spread on the molybdenum substrate, and high-purity argon is used for protection, and the oxygen content in the construction room is ≤0.05%. The laser melting parameters of the selected area are set as follows: the laser power E is 380W, the scanning speed v is 300mm/s, the scanning distance h is 20μm, and the scanning layer thickness is 30μm. . Finally, molybdenum metal parts with complex shapes are obtained, and the density is >98.9%.

Example 2

The raw material powder is polycrystalline molybdenum powder with an average particle size of about 30 μm, a total of 15 kg, and a counter-jet jet milling device is used. The pressure of the grinding chamber is set at 0.5-1.0 MPa, and nitrogen gas is used as the grinding medium so that the oxygen content in the grinding chamber is ≤0.5%. The first jet mill is processed at 45-60Hz, the second jet mill is treated at 30-45Hz, the third jet mill is treated at 15-30Hz, and finally a nearly spherical molybdenum powder with an average particle size of about 26μm is obtained. The obtained molybdenum powder is put into a tube furnace, fed with high-purity hydrogen, and reduced for 60-120 minutes under the conditions of 600-650°C and a heating rate of 7°C/min. Use 3D Max software to draw a three-dimensional schematic diagram of the part, then set the processing parameters, and export the parameter file in Materialize Magics software. Clean the feed tank, powder feeder, powder spreader and substrate with absolute ethanol, and blow dry with a hair dryer. Purge the build chamber and residue recovery tube with an argon gun. The reduced mixed molybdenum powder is loaded into the powder feeding tank, and then a layer of powder with a thickness of about 50 μm is spread on the molybdenum substrate, and high-purity argon is used for protection, and the oxygen content in the construction room is ≤0.05%. The laser melting parameters of the selected area are set as follows: the laser power E is 380W, the scanning speed v is 400mm/s, the scanning distance h is 50μm, and the scanning layer thickness is 35μm. . Finally, molybdenum metal parts with complex shapes are obtained, and the density is >98.5%.

Example 3

The raw material powder is polycrystalline molybdenum powder with an average particle size of about 30 μm, a total of 15 kg, and a counter-jet jet milling device is used. The pressure of the grinding chamber is set to 0.6MPa, and nitrogen is used as the grinding medium so that the oxygen content in the grinding chamber is ≤0.5%. The first jet mill was processed at 45Hz, the second jet mill was processed at 45Hz, the third jet mill was processed at 30Hz, and finally a nearly spherical molybdenum powder with an average particle size of about 30 μm was obtained. The obtained molybdenum powder is put into a tube furnace, fed with high-purity hydrogen, and reduced for 60-120 minutes under the conditions of 600-650°C and a heating rate of 7°C/min. Use 3D Max software to draw a three-dimensional schematic diagram of the part, then set the processing parameters, and export the parameter file in Materialize Magics software. Clean the feed tank, powder feeder, powder spreader and substrate with absolute ethanol, and blow dry with a hair dryer. Purge the build chamber and residue recovery tube with an argon gun. The reduced mixed molybdenum powder is loaded into the powder feeding tank, and then a layer of powder with a thickness of about 50 μm is spread on the molybdenum substrate, and high-purity argon is used for protection, and the oxygen content in the construction room is ≤0.05%. The laser melting parameters of the selected area are set as follows: the laser power E is 380W, the scanning speed v is 400mm/s, the scanning distance h is 50μm, and the scanning layer thickness is 35μm. . Finally, molybdenum metal parts with complex shapes are obtained, and the density is >99.5%.

Example 4

The raw material powder is polycrystalline molybdenum powder with an average particle size of about 30 μm, a total of 15 kg, and a counter-jet jet milling device is used. The pressure of the grinding chamber is set to 0.9MPa, and nitrogen is used as the grinding medium so that the oxygen content in the grinding chamber is ≤0.5%. The first jet mill was processed at 45Hz, the second jet mill was processed at 30Hz, the third jet mill was processed at 15Hz, and finally a nearly spherical molybdenum powder with an average particle size of about 21 μm was obtained. The obtained molybdenum powder was put into a tube furnace, fed with high-purity hydrogen, and reduced for 60 minutes at 600°C and a heating rate of 7°C/min. Use 3DMax software to draw a three-dimensional schematic diagram of the part, then set the processing parameters, and export the parameter file in Materialize Magics software. Clean the feed tank, powder feeder, powder spreader and substrate with absolute ethanol, and blow dry with a hair dryer. Purge the build chamber and residue recovery tube with an argon gun. The reduced mixed molybdenum powder is loaded into the powder feeding tank, and then a layer of powder with a thickness of about 50 μm is spread on the molybdenum substrate, and high-purity argon is used for protection, and the oxygen content in the construction room is ≤0.05%. The laser melting parameters of the selected area are set as follows: the laser power E is 380W, the scanning speed v is 400mm/s, the scanning distance h is 50μm, and the scanning layer thickness is 40μm. . Finally, molybdenum metal parts with complex shapes are obtained, and the density is >99%.

The above description is only an implementation example of the present invention, and does not limit the scope of patent application of the present invention. Any direct or indirect application in other related technical fields, or the equivalent structure or similar production process made by using the contents of the description of the present invention, All will be included in the patent protection scope of the present invention.

Claims (5)

1. a kind of method for preparing the pure molybdenum part of high-performance, it is characterised in that: obtained first using multiple airflow milling technical treatment To be uniformly dispersed, the near spherical molybdenum powder of narrow particle size distribution, then molybdenum powder is restored in the high temperature furnace of atmosphere of hydrogen, is obtained The reduction molybdenum powder of low oxygen content and good fluidity；The near spherical molybdenum powder of different-grain diameter after airflow milling is mixed；Meanwhile passing through meter Calculation machine modeling software designs the workpiece schematic diagram of complicated shape and controls scanning speed, sweep span, Scan slice thickness and sweep Direction is retouched, mimeograph documents are exported；Clean the powder feeding tank of precinct laser fusion equipment, Photocopy Room, it is ensured that the pure no dirt of printing environment Dye；Then, powder is packed into SLM device and imports the molybdenum part that mimeograph documents prepare complicated shape, specific process step Are as follows:

Step 1: handle using to spray formula air-flow mill apparatus raw material molybdenum powder, set grind cavity pressure as 0.5~ 1.0MPa employs nitrogen as abrasive media, makes oxygen content≤0.5% in grinding chamber, is 15~60Hz in the frequency of separation wheel In the range of molybdenum powder is handled；Using jet milling process three times, i.e., first time airflow milling is in 45~60Hz high frequency to molybdenum powder Tentatively dispersed and shaping, second of airflow milling disperses molybdenum powder and shaping again in 30~45Hz intermediate frequency, third time Airflow milling in 15~30Hz low frequency further to molybdenum powder shaping and partial size sieves, finally obtain average particle size distribution uniformly, granularity Narrowly distributing, well dispersed near spherical molybdenum powder；

Step 2: powder reduction: by airflow milling, treated that mixing molybdenum powder is put into tube furnace, is passed through high-purity hydrogen, in 600~ 650 DEG C, heating rate be 7 DEG C/min under conditions of reduction 60~120min obtain the molybdenum powder of low oxygen content；

Step 3: using 3D Max Software on Drawing part schematic three dimensional views first, then machined parameters are set, in Materialise Magics software derived parameter file；

Step 4: model file is imported computer system first, airflow milling is handled using SLM precinct laser fusion equipment And the molybdenum powder after restoring is loaded into powder feeding tank, then spreads the powder that thickness is about 50 μm in molybdenum base plate, is carried out using high-purity argon gas Protection can start laser scanning after building indoor oxygen content≤0.05%, realize whole full-automatic printing forming, final to obtain To complicated shape and high-densit molybdenum part.

2. the method for the preparation pure molybdenum part of high-performance according to claim 1, it is characterised in that: the target height causes Density molybdenum part, purity are 99.99% or more, and consistency is up to 98% or more.

3. the method for the preparation pure molybdenum part of high-performance according to claim 1, it is characterised in that: using airflow milling three times Molybdenum powder average particle size distribution after process is narrow, and powder is well dispersed, and subsphaeroidal, good fluidity, specific surface area is presented in pattern Increase, sintering activity improves, and can get good molten bath, improves print quality.

4. the method for the preparation pure molybdenum part of high-performance according to claim 1, it is characterised in that: restored using tube furnace Oxygen content≤0.01% of molybdenum powder afterwards.

5. the method for the preparation pure molybdenum part of high-performance according to claim 1, it is characterised in that: each work ginseng of SLM Number are as follows: laser power E be 380W, 200~700mm/s of scanning speed, 80~120 μm of sweep span, 30~50 μm of Scan slice thickness, Cabin oxygen content≤0.05% is built, scanning strategy can weaken crack propagation behavior using 45 ° of rotations alternately grid type scanning, Balanced residue stress obtains high performance pure molybdenum part.